You can only Opt-Out of the inclusive access program through the deadline listed on the Course Materials page in your course. After this deadline, you can no longer Opt-Out.
You can Opt-In again up through that deadline as well. As long as you see Opt-In as an option on the Course Materials page, you can Opt-in again. Once the deadline has passed, this option will be removed and you will no longer be able to Opt-In or Opt-Out.
While the deadline for opting-out is strict, if you accidentally Opted-Out and want to Opt-In again, you may have some more time. Please contact your bookstore manager for assistance.